The compound, levovirin, is a known antiviral agent having the formula: 
Levovirin has been produced from β-tetraacetyl-L-ribofuranose, the β-anomer of a compound of the formula: 
In accordance with prior procedures, the β-anomer of the compound of Formula II, i.e., the compound of Formula II-A, is converted to levovirin by the following reaction scheme: 
In this reaction scheme, the pure β-tetraacetyl-L-ribofuranose (the compound of Formula II-A) is used as the starting material. Although pure β-tetraacetyl-L-ribofuranose is commercially available, its price is high. Therefore, the cost of levovirin produced by this method has been expensive. In view of the fact that the compound of Formula II-A is difficult to produce inexpensively, this also has been a major problem with this synthesis.
As disclosed in Ramasamy, Tam, et al., J. Med. Chem., 43:1019 (2000), the compound of Formula II-A has been produced from L-ribose which has the formula: 
This synthesis has involved eight evaporation to dryness steps and sixteen extraction operations to produce the compound of Formula II-A in pure form for its conversion to the compound Levovirin. This process has not been suitable for scale up.
In 1968, Guthrie and Smith in Chem., Ind., 547-548 (1968) proposed a method for converting D-ribose into β-tetra-O-acetyl-D-ribofuranose, an enantiomer of the compound of Formula II-A. This method contained three chemical transformations, the acetal formation, acetylation, and acetolysis. Ramasamy et al's synthesis followed Guthrie's synthetic strategy in which the acetal formation was effected in MeOH and HCl, the acetylation was carried out with acetic anhydride in pyridine, and the acetolysis was conducted in acetic acid and acetic anhydride in the presence of concentrated sulfuric acid. The crude product was a mixture of α/β-anomers of tetra-O-acetyl-L-ribofuranose and the pure β-anomer of tetra-O-acetyl-L-ribofuranose was obtained in 57% overall yield via recrystallization from ethyl ether.
This cumbersome procedure producing poor yields was considered necessary since it was believed that only the β-anomer of Formula II-A could be used in the synthesis of levovirin of Formula I. Therefore, in this procedure, the compound of Formula II-A had to be purified and separated from its α-anomer, the compound of Formula II-B 
Therefore, under the prior procedures, it was believed that it was necessary to separate and remove the compound of Formula II-B from the compound of Formula II in order to carry out this synthesis. This has involved costly separation techniques and led to reduced yields. In summary, these processes have made the production of the compound of Formula I costly.